Status of the Project and Physics of the Spallation Target
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PHYSOR 2004 -The Physics of Fuel Cycles and Advanced Nuclear Systems: Global Developments Chicago, Illinois, April 25-29, 2004, on CD-ROM, American Nuclear Society, Lagrange Park, IL. (2004) The TRADE Experiment: Status of the Project and Physics of the Spallation Target C. Rubbia1, P. Agostini1, M. Carta1, S. Monti1, M. Palomba1, F. Pisacane1, C. Krakowiak2, M. Salvatores2, Y. Kadi*3, A. Herrera-Martinez3, L. Maciocco4 1ENEA, Lungotevere Thaon di Revel, 00196 Rome, ITALY 2CEA, CEN-Cadarache, 13108 Saint-Paul-Lez-Durance, FRANCE 3CERN, 1211 Geneva 23, SWITZERLAND 4AAA, 01630 Saint-Genis-Pouilly, FRANCE The neutronic characteristics of the target-core system of the TRADE facility have been established and optimized for a reference proton energy of 140 MeV. Similar simulations have been repeated for two successive upgrades of the proton energy, 200 and 300 MeV, corresponding to different performances and design requirements and different characteristics of the proposed cyclotron and, as a consequence, of the proton beam. An extensive comparison of the main physical parameters has been also carried out, in order to evaluate advantages and disadvantages of different proton beam energies in the design of the spallation target and to allow the optimal engineering design of the whole TRADE facility. KEYWORDS: TRADE facility, ADS, Spallation target physics, Experimentation, External neutron sources, intermediate proton energy. 1. Introduction The TRADE “TRiga Accelerator Driven Experiment”, to be performed in the existing TRIGA reactor of the ENEA Casaccia Centre, has been proposed as a major project in the way for validating the ADS concept. Actually, TRADE will be the first experiment in which the three main components of an ADS – the accelerator, the spallation target and the sub- critical blanket – will be coupled at a power level sufficient to appreciate feedback reactivity effects. As such, the TRADE experiment represents the necessary intermediate step in the development of hybrid transmutation systems, its expected outcomes being considered crucial – in terms of proof of stable operability, dynamic behavior and licensing issues – for the subsequent realization of an ADS Transmutation Demonstrator. As already shown in previous papers [1,2], the experiments of relevance that can be performed in TRADE concern: ∑ the dynamic system behavior of an ADS vs. the neutron importance of the external source at different sub-criticality levels, thus providing important information on the optimal sub-criticality level; ∑ Sub-criticality measurements at significant power; ∑ Correlation between reactor power and proton current; ∑ Reactivity control (neutron source importance method); ∑ Compensation of power effects of reactivity swing with control rods movements or with proton current variation; ∑ Start-up and shutdown procedures, including suitable techniques and instrumentation. * Corresponding author, Tel. +41-22-767-9569, FAX +41-22-767-7555, E-mail: [email protected] In this paper, we will present the status of the project, as well as results of recent simulations and analyses concerning the physics of the spallation target for different values of the proton energy, from 140 MeV up to 2-300 MeV. 2. Status of the Project The TRADE experiment - aimed at a global demonstration of the ADS concept - is an original idea of Carlo Rubbia developed through a feasibility study carried out by an ENEA and CEA Working Group over 2001-beginning of 2002. These feasibility studies have been followed by further conceptual design activities performed in 2002-2003 by an International TRADE collaboration set up by ENEA (Italy), CEA (France), FZK (Germany), DOE (USA), CIEMAT (Spain), CNRS (France), AAA (France), and ANSALDO (Italy). The overall layout of the facility - selected after a quite comprehensive comparison among others - is shown in Figure 1 [3]. It foresees the erection of a new bunker, close to the existing TRIGA building, to house the accelerator and the test station for proton beam test and adjustment. The proton beam is transferred from one building to the other via a section of the transfer line that is particularly simple, since the cyclotron is at the same level of the top of the reactor. The beam transport line is protected by a massive shielded tunnel which extends into the TRIGA building up to the reactor top. Through the straight section of the transport line, the beam is transferred to the final bending section composed of two magnetic dipoles and three magnetic quadrupoles, which have the duty of directing the beam, with the correct size, to the spallation target placed in the central thimble of the reactor. Fig.1 Reference layout of the TRADE facility (vertical section) The studies performed so far by the TRADE International Collaboration have concerned: ∑ The neutronics of selected possible configurations, along with a neutronic benchmark to define codes and tools to be used for the neutronic design and the interpretation of the experimental measurements; ∑ The core and target thermal hydraulics, using both natural or forced convection, including the target coupling to the reactor at power; ∑ The target performances and characteristics as well as the conceptual design of the target, its cooling system and the definition of the tests needed for its qualification; ∑ A conceptual design of the Beam Transport Line; ∑ The shielding and activation aspects in order to gain insight on the dose issues. ∑ The safety and licensing aspects related to the plant modifications induced by the TRADE experiment, including considerations on general safety criteria, possible accident initiators and a preliminary hazards analysis; ∑ The overall experimental program to be performed in TRADE; ∑ The representativity of the foreseen experiments in terms of dynamic behaviour, neutron spectrum, reactivity control, proton current/power relation, operation at start- up and shut-down, external source importance measurements, etc.. ∑ A preliminary cost and time schedule evaluation. Furthermore, a preliminary experimentation in the TRIGA RC1 reactor was carried out in fall 2002, to characterize the TRADE reference core; a new experimental phase - which will include measurements in a mock-up of the TRADE core with Californium, DD and DT external sources – is being performed over 2003-2004 (reported in another paper at this conference). As for the accelerator, several configurations were studied for a suitable proton energy beam of 140, 200 and 300 MeV and with a beam current in the range 100-300 µA. Taking into account the constraints related to the cost and the relatively short time scale for the implementation of the TRADE experiment, a room temperature H- cyclotron is considered the most affordable solution. Actually, even if the requested performances for TRADE (140 MeV, 2-300 µA) are rather challenging with respect to the ones of the existing machines, the TRADE cyclotron can be regarded as an evolution of a typical H- machine for radioisotope production (Ep around 30 MeV) or for hadron-therapy (Ep around 60 MeV). As for international agreements to implement the TRADE experiment, a Memorandum of Understanding (MOU) among “funding” partners - ENEA, CEA, DOE and FZK – was signed in 2003 by ENEA, CEA and FZK. TRADE-PLUS – the part of the TRADE project devoted to the design of the facility as well as to the experiments and their interpretation and transposition to the future ADS Demonstrator - is also one of the major subprojects of the Integrated Project EUROTRANS, which is being presented to the European Commission by several European associations within the EURATOM 6th Framework Programme in the Thematic Priority Area “Management of Radioactive Waste: Transmutation”. 3. Physics of the Spallation Target The spallation target is the key component of any ADS concept. Even in the TRADE facility, despite the relative small power of the proton beam (<40 kW), the development and design of the target implies a detailed assessment of different aspects mutually interacting, from the physics of spallation reaction - including neutron generation and distribution, spallation products yields and damage rates – to technological issues, such as choice of the most suitable material, power density distribution, heat removal, thermo-mechanics, fabricability, etc. In particular, accurate and rigorous assessment of nuclear parameters under different physical conditions is the prerequisite for an optimal design of the target and its interaction with the (subcritical) TRIGA core. This work aims at evaluating, by probabilistic transport codes (FLUKA and EA-MC), the main neutronic and physical parameters such as yield and energy and angular distribution of the spallation neutrons, proton and neutron flux around the target, energy deposition, radiation damage, spallation product yields and radioactivity. The calculations have been performed for different intermediate energies (140, 200 and 300 MeV) of the proton beam impinging on a solid Tantalum target, allowing the evaluation of pros and cons of different solutions as well as the most suitable cyclotron for the TRADE facility and its successive utilizations. The performances and the impact on the target design of different shapes of the proton beam and geometrical configurations of the spallation target have been also assessed. The guidelines which have been followed for the target development together with the main constraints and interfaces have been extensively discussed in ref. [4]. The geometry is described below to provide